1. Field of the Invention
The present invention relates to a surge current prevention circuit of a microwave oven, and more particularly to a surge current prevention circuit of a microwave oven adapted to prevent an erroneous operation of a microwave oven which occurs when a surge current generated at an initial operation stage of the microwave oven is infused into a high-voltage transformer.
2. Description of the Prior Art
Generally, a driving circuit of a microwave oven provided with a surge current prevention circuit according to the prior art comprises, as illustrated in FIG. 1, a filtering unit 10, a fan motor 15, a surge current prevention circuit 20, and a high voltage transformer 30.
As illustrated in FIG. 1, the filtering unit 10 serves to eliminate higher harmonics included in a commercial alternating current (AC) voltage supplied through input terminals (A, B). The fan motor 15 receives the AC voltage supplied through the filtering unit 10 from the input terminals (A, B) and is driven thereby to rotate a cooling fan (not shown).
Furthermore, the surge current prevention circuit 20 is provided to prevent a surge current which is generated at an initial operation stage of a microwave oven, where the circuit includes a surge resistor 23, a surge coil 25 and a high voltage alternating current type surge relay 27. A high voltage transformer 30 receives a commercial alternating current AC voltage supplied through the input terminals (A, B) to transform same to a predetermined voltage and to drive a magnetron (not shown).
In the driving circuit thus described, when a user inputs a start key, higher harmonic components are removed by the filtering unit 10 to thereafter be supplied to the fan motor 15 and the surge current prevention circuit 20.
Next, when the cooling fan is rotated, the surge coil 25 starts to be excited by the commercial AC voltage, which is then supplied to the transformer 30. By this, the surge current generated at an initial operation stage of the microwave oven is limited in the course of passing through the surge resistor 23.
Next, when the initial operation stage is over, the surge coil 25 is excited to switch on or switch off the surge relay 27 into an on-state, and by this, the filter commercial AC voltage is directly supplied to the high voltage transformer 30 bypassing the surge resistor 23.
Next, the transformer 30 receives the filtered AC voltage to supply same to the magnetron, which in turn generates microwaves to heat and cook a food article.
In other words, the surge current generated at the initial operation stage of the microwave oven is limited in the course of passing the surge resistor 23, and after the initial stage is over, the filtered commercial AC voltage passes the surge relay 27 to be directly supplied to the high voltage transformer 30.
However, there is a problem in the surge current prevention circuit according to the prior art in that the surge coil is excited by the high voltage of commercial AC voltage, by way of example, 100-200V, to switch on or switch off the surge 27. Also, the component costs of such a surge prevention circuit tend to be high, thereby increasing manufacturing cost and consumed electricity.
There is another problem in that the microwave oven is unstably operated due to inconstant switching operation time.